1. Field of the Invention
This invention relates to improvements in guidance systems and, more particularly, to improvements in guidance systems of the type in which a probe is used for detecting and following a path defined by surfaces having vertical and horizontal components.
2. Description of the Prior Art
Systems for guiding apparatus along a path defined by surfaces having vertical and horizontal components are particularly useful, for example, in guiding a welding head, torch, or the like, along the junction between two or more pieces of material to be welded or bonded together with a lap, butt or shaped butt joint having a groove, or the like. Such guiding systems frequently employ a probe, for detecting the juncture to be welded, mounted directly on the welding head or torch which follows the probe as a slave, or the like.
In one common apparatus, for example, the pieces of material to be welded together are placed in the desired relative position, then moved past the welding apparatus, which performs the desired welding operation upon them. As the pieces are moved, the probe, riding, for example, within a groove wherein the weld is to be effected, detects changes in the general direction of the groove or deivations in the surface defining the groove and transmits a signal or signals to the associated apparatus to correct the path of the welding head and the probe itself, if it be mounted on a separate cross-slide apparatus of its own.
The probes employed on such systems usually include an elongated wire, shaft, or rod, mounted essentially coaxially within a body, frame or housing. The outer or exposed tip or finger of the wire shaft or rod rides or tracks within the groove or along the seam wherein or whereat the weld is to be effected. The opposite end of the wire, shaft or rod is disposed within the probe housing and is adapted to close (or open) a circuit to the respective positioning motor in accordance with the response of the movement of the top or finger as it travels along the groove or seam to be welded.
More particularly, the tip or finger is axially displaced, vertically and/or horizontally, as it comes into contact with the walls of the groove or seam and the opposite end is thereby caused to engage or disengage, if the probe is biased in the direction of movement, appropriate switches which actuate or deactuate the corresponding motor to position the torch in accordance with the path sensed by the probe tip.
Thus, the positioning motors are either in or out of operation and the cross-slides are either inoperable or operating at a fixed speed, without regard to the size or degree of the deviation from or change in the path of the seam (and, therefore, the probe) relative to basic direction of advance, horizontally and vertically, of the probe.
Alternatively, as shown in U.S. patent application Ser. No. 874,153 filed Nov. 5, 1969, the top or remote end of the probe is positioned to operate two switches controlling the movement of the positioning motor in one direction. In this instance a small change or deviation in the path of the particular component (horizontal or vertical) (i.e., relatively small movement of the tip or finger) actuates one switch supplying a low voltage to the motor with the result that a low correctional speed results and a larger movement of the tip or finger actuates the second switch to supply a larger voltage to the positioning motor which then operates the cross-slide at a second higher speed. Thus, providing a two-speed correction device.
Other prior art devices, such as that shown in U.S. Pat. No. 3,594,540, have suggested using a rotating switch carried at the top of the probe and adapted to vary the voltage delivered to the positioning motor by varying the position of the switch in accordance with the degree of change or deviation.
These and other prior art devices also experienced loss of desired welding results because of the inertia inherent in the apparatus for positioning both the welding head or torch and the probe itself. Such inertia evidences itself both in delay in initiating corrections and in problems of stopping correctional movements, once correction is effected, i.e., overshooting.
With respect to the latter problem, some prior art devices lacked a positive braking mechanism and none provided effective means for braking the correctional movement in proportion to degree and/or speed of correction and in accordance with the magnitude of or attained by the correctional response.
Thus, the problem of coordinating the speed of correction with the degree of deviation or correction required has been recognized in the prior art, but none of the prior art devices suggested nor disclosed structure by which the same could be obtained in apparatus adapted to both seek and follow the seam and to correct for deviations without regard to their direction relative to the nominal basic direction of the guide surfaces and direction of movement of the detecting device and welding head. The problem is further aggravated when a deviation is large, especially transversely of the direction of the basic path, as the torch frequently advances longitudinally past the deviation before it has moved laterally, sufficient to "cover" the deviation.
And, further, none of the prior art devices has, in fact, proven effective in the art and on a commercial basis.